Objective: To determine if a cognitive summary score (CSS) is sensitive in detecting early cognitive deficits in de novo Parkinson’s disease (PD).

Background: Cognitive impairment is common in PD, even in de novo or early disease. However, the ability to track cognitive changes over time, including in clinical trials, is hampered by consensus over which neuropsychological tests to use, and how to utilize the results. An option that allows one to combine the richness and details of a neuropsychological battery with the simplicity of a single test score is to create a CSS after all detailed test results are normed on the same scale.

Method: Using baseline cognitive data from PD participants and healthy controls (HC) enrolled in the PPMI, the following steps were taken: (1) clean test score data; (2) determine which test scores to utilize for the CSS (6 scores across 5 tests assessing multiple cognitive domains); (3) transform standardized scores to z-scores; (4) create final HC and super healthy control (SHC) groups; (5) create regression-based internally-derived standardized scores from SHC group; and (6) create CSS by averaging all standardized test scores.

Results: Using raw scores, the PD group scored worse than the HC/SHC groups on nearly all tests (Table 1). Similarly, the PD scored worse than the HC/SHC groups, with a larger effect size for the SHC group, whether using published (Table 2) or internally-derived (Table 3) norms, with the biggest effect sizes for processing speed and verbal episodic memory. Using internally-derived norms generated similar results (Tables 2 and 3), with the additional effect of decreasing the standardized scores in both the PD and HC/SHC groups. Finally, the CSS had a larger effect size (PD vs. HC/SHC) than all individual tests except processing speed (Table 4).

Conclusion: PD patients perform worse cognitively than HC at disease diagnosis on all cognitive domains, most notably processing speed and verbal memory. Using a SHC group increased effect sizes, and using internally-derived norms lowers the scores of PD patients to “expected” levels. A SCC performed as good or better than all individual cognitive tests, and combines the richness of a detailed, multi-domain cognitive battery with the simplicity a single, equally-weighted score.

Table 1

Table 2

Table 3

Table 4

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MDS Abstracts - https://www.mdsabstracts.org/abstract/creation-and-performance-of-a-cognitive-summary-score-in-de-novo-parkinsons-disease-results-from-the-ppmi-study/